Emerging cancer nanotechnology enables target-delivery of substantial payloads of drugs to cancer sites with concomitant reduction of side-effects due to the lesser accumulation in the critical organs. This prompts loading of nanocarriers with therapeutic cargo and contrast agents, allowing combined cancer therapy and tumor visualization, respectively. Researchers from Lobachevsky University of Nizhny Novgorod, Russia, have implemented such combined therapy using conjugates of radionuclide yttrium-90-doped upconversion nanoparticles (UCNP) and targeted toxin. The resultant hybrid theranostic complex showed high therapeutic efficacy and high imaging contrast both in vitro and in vivo. More specifically, the developed complex addresses oncotherapy of HER2 positive cancers.

Core of the complex represents an UCNP. Owing to their unique photophysical properties, UCNPs are widely used as a platform for assembling theranostics complexes. Conversion of deeply-penetrating in biological tissue near-infrared light (NIR) to the higher photon-energy visible, ultraviolet and NIR light is among UCNP most useful properties.

The developed theranostic complex carries two toxic modules – beta emitter 90Y and targeted toxin DARPin-PE40, which exert toxic effects on tumor cells by different mechanisms. A strong synergism in the toxic effect was observed upon the use of two toxic modules, i.e. the total effect of the two toxicants was more than an order of magnitude greater than a sum of the separate toxic effects. “We speculate the targeted toxin blocks protein synthesis in the cells, while a beta-emitter 90Y causes the formation of free radicals and reactive oxygen species in the cells, along with direct damage of macromolecules. A significant increase in the toxicity of theranostic complex compared to its individual modules was due to damage of the protein synthesis involved in the antioxidant protection and repair of the ionizing radiation-mediated damage”, – Dr. Vladimir Vodeneev explains.

Tumors are typically characterized by cellular heterogeneity. Oncotherapy based on administration of mono-drugs suffers from poor therapeutic efficacy, in addition to the development of multiple drug resistance. The designed theranostic complex featuring two toxic modules of differing therapeutic actions are believed to be more potent in the treatment of heterogeneous tumors with reduced drug resistance.

The produced theranostic complex was capable to inhibit the growth of xenograft tumors upon an intratumoral administration. Apparently, this effect was due to the local action of both therapeutic agents and their long-term retention in the tumor, and because of a larger dose of the ionizing radiation absorbed by the tumour tissue. The obtained results show promise for effective combined oncotherapy leading to prospective translation to clinical practices.